Study on the diffusion fluxes of dissolved inorganic nitrogen phosphorus and urea across sediment-water interface in scallop culture area of Changli coastal waters

Three cruises were conducted in the scallop cultivation area of Changli coast in December 2015, April and September 2016; respectively, to collect the sediment cores and in situ bottom seawater. The diffusion fluxes of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and urea across sediment-seawater interface were measured by incubation experiment in laboratory. The average diffusion fluxes of DIN, DIP and urea across sediment-water interface were 52.72 μmol/(m²·h), 0.074 μmol/(m²·h) and 1.00 μmol/(m²·h), respectively, which showed obvious diffusion trend of nutrient from sediment to overlying water. The diffusion flux of urea in Changli scallop culture area was two to three-folds of that in Jiaozhou Bay and more than twice as much as that in Yellow Sea, which increased the possibility of brown tides caused by Aureococcus Anophagefferens. The annual fluxes of DIN, DIP and urea from sediment to water were estimated to be 1680.73 t, 2.36 t and 136.66 t respectively, which indicated that sediment was a major source for nutrient input, especially for DIN and urea.